An LCD has the advantages of portability, low power consumption, and low radiation, and has been widely used in various portable information products such as notebooks, PDAs (personal digital assistants), video cameras and the like. Furthermore, the LCD is considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
Normally, an LCD includes an LCD panel, a backlight module configured for illuminating the LCD panel, and a PCB module configured for providing operation voltages respectively to the LCD panel and the backlight module. The PCB module can also receive image signals from an external circuit such as a computer, and transform the image signals into image driving data. The image driving data drive the LCD panel of the LCD to display corresponding images.
FIG. 4 is a block diagram of a typical PCB module which can be used in an LCD. The PCB module 10 includes a power source circuit 11 configured for outputting operation voltages, a backlight control circuit 12 configured for driving a backlight of the LCD, and a signal processing circuit 13 configured for receiving image signals from an external circuit (not shown) such as a computer or a DVD (digital video disc) player. The signal processing circuit 13 transforms the image signals into image data that an LCD panel of the LCD can receive, and then transmits the image data to the LCD panel.
FIG. 5 is a circuit diagram of the signal processing circuit 13. The signal processing circuit 13 includes a crystal oscillating circuit 130, a low voltage transformer 131, a voice-frequency circuit 132, a scaler 133, an MCU (micro controller unit) 134, an EDID (extended display identification data) memory 135, a work mode memory 136, a video input interface circuit 137, a panel interface circuit 138, and a keyboard interface circuit 139.
Operation voltages generated by the power source circuit 11 are provided to the low voltage transformer 131, the panel interface circuit 138, the MCU 134, and the voice-frequency circuit 132. The low voltage transformer 131 provides voltages to the scaler 133.
The video input interface circuit 137 receives video signals and a symbol signal from the external circuit, and respectively provides the video signals and the symbol signal to the scaler 133 and the EDID memory 135.
The scaler 133 receives the video signals from the video input interface circuit 137, and decodes the video signals into image data and sound signals. The image data are provided to the panel interface circuit 138. The sound signals are provided to the voice-frequency circuit 132.
The voice-frequency circuit 132 transforms the sound signals into audible sounds (including voice) using a speaker (not shown). Operation of the voice-frequency circuit 132 is controlled by the MCU 134.
The EDID memory 135 stores symbol information of the LCD. The EDID memory 135 also receives the symbol signal from the video input interface circuit 137, and provides the symbol information and the symbol signal to the MCU 134. The MCU 134 compares and identifies the symbol information and the symbol signal.
The work mode memory 136 stores parameters which corresponds to at least one work mode of the LCD. The parameters can be provided to the MCU 134, thus the MCU 134 can adjust the work mode of the LCD.
The keyboard interface circuit 139 receives an interrupt signal from an adjusting button of the LCD when the adjusting button is pressed by a user. The interrupt signal is then provided to the MCU 134. Thus the contrast, brightness, and vertical and horizontal sizes of images displayed by an LCD panel of the LCD can be adjusted or changed by the MCU 134 when the user pushes the adjusting button and thus generates the interrupt signal.
The crystal oscillating circuit 130 generates a pulse clock signal having a state frequency, and provides the pulse clock signal to the MCU 134 and the scaler 133.
The panel interface circuit 138 provides the image data received from the scaler 133 and the operation voltages received from the power source circuit 11 to the LCD panel.
Normally, the signals that the signal processing circuit 13 deals with are digital signals each having high frequencies. In order to depress or eliminate interference between different digital signals that have different high frequencies, the PCB module 10 is typically constituted in a double-layer PCB. Because the cost of the double-layer PCB is high, the cost of the PCB module 10 is correspondingly high. Furthermore, because the signal processing circuit 13 is integrated in the double-layer PCB, when one of internal circuits of the signal processing circuit 13 such as the scaler 133 needs to be changed, a layout of the signal processing circuit 13 or even of the entire PCB module 10 needs to be redesigned. The need to change one of the internal circuits may arise, for example, when the PCB module 10 is to be used together with another type of LCD panel in mass manufacturing. In this respect at least, the PCB module 10 having the signal processing circuit 13 can be considered to increase the cost of mass manufacturing different kinds of LCDs having different LCD panels.
It is desired to provide a PCB module which can overcome the above-described deficiencies.